PROBOSCIDEANS 213 



cementum four to five millimeters in thickness. In the anterior two- 

 thirds of the grinding surface the enamel is looped back and forth from 

 the outer edges to the middle in the manner represented in figure 6, plate 

 148, of Owen's Odontography, a figure described as showing "the more 

 normal form and structure" of the molars of Elephas primigenius. This 

 arrangement of the enamel seems, however, to be rather unusual. One 

 other tooth in our collections, which was taken from gravels near West 

 Union, Iowa, in 1875, has the enamel disposed in this way. Of the many 

 molars of Elephas primigenius, figured in part II of A. Leith Adams' 

 "Monograph on British fossil elephants," there is just one — figure 1, 

 plate XIV — that shows this feature, and in this case the looping is 

 limited to the anterior third of the grinding surface. The tooth figured^ 

 by Adams, like the Denison tooth, is the "right upper last true molar," 

 but his must have belonged to an animal smaller than the Towa form. 



At the meeting of the American Association for the Advancement of 

 Science, in Dubuque, in 1872, the writer had the privilege of seeing the 

 tooth, which Foster regarded as the type of a new species of fossil ele- 

 phant, Elephas indianapolis, and of hearing his description of it, and one 

 at least of the distinguishing characters of the supposed new species was 

 the looping of the enamel from the middle of the grinding surface to the 

 sides, instead of the usual arrangement of this tissue in elongated ellipses 

 surrounding plates of dentine.^ In the bibliography and catalogue of the 

 fossil vertebrata of North America, by Hay, Bulletin of the United States 

 Geological Survey, No. 179, page 714, the tooth described by Foster is 

 assumed to be one of the forms of molars of Elephas primigenius. 



The extent to which silicification has progressed in the large tooth and 

 adhering bone from Denison is not so great as in the fossils certainly 

 known to be Aftonian. For the present the age may be left undecided. 

 It is possible, however, that Elephas primigenius belongs to a stage more 

 recent than the Aftonian, and that it was not contemporaneous with the 

 Equus and Elephas imperator fauna. 



MASTODON 



The new collections contain a number of teeth of Mastodon americanus, 

 but the most important addition to the mastodon series is a massive lower 

 jaw from Missouri Valley (plates 21 and 22). The ascending branch is 



^Elephas indianapolis, a new species of fossil elephant, by J. W. Foster. Proceedings 

 of the American Association for the Advancement of Science, twenty-first meeting, held 

 at Dubuque, August, 1872, p, 259. The title only is printed in the Proceedings. After 

 the reading of the paper, and at the suggestion of some of the naturalists present, 

 Poster proposed to change the name to Elephas mississippiensis, and under this designa- 

 tion there is a short reference to the paper and the proposed species in Nature, vol. vi, 

 p. 443. 



